In the field of packaging machines for various types of articles, and in particular for rolls of paper of the so-called “tissue” type, for example absorbent paper or toilet paper, machines are widespread which are capable of packaging a predefined number of rolls, arranged according to the multiple rows and layers configuration that is commonly sold to the final consumer.
According to a known constructive solution, these machines are provided first of all with roll feeders, which are controlled by movement means, for example conveyor belts or platforms, along which there are distribution elements capable of arranging the rolls in the desired configuration.
Subsequently, the rolls thus ordered are sent to a traction unit, which moves them while the subsequent steps of the execution of the wrapping cycle are performed on them.
More particularly, appropriately provided and shaped elements wrap the rolls by means of a film; heat-sealing heads then complete the wrapping cycle and ensure the closure of the package by acting on the folded flaps of film.
Typically, such traction units are provided with a motor that is capable of moving a plurality of grip elements along a substantially annular path.
The above-mentioned grip elements are provided with a series of mutually opposite teeth capable of clamping the rolls during their movement. In order to adapt to the various formats that can be provided for the package to be provided, the traction unit must be equipped with means for adjusting the grip elements and the teeth in particular, whose position must be adapted to the different dimensions of the assembly to be moved.
According to a known constructive solution, the grip elements are constituted by sliders carried by carriages, which are arranged transversely with respect to the advancement direction; the teeth that retain the rolls extend from the sliders at right angles with respect to the plane of the carriages (in this manner it is possible to arrange a plurality of sliders along the same carriage, so that each grip element is in practice composed of multiple teeth arranged side by side).
The adjustment means are constituted by toothed belts or chains, which wind around pulleys that can move transversely with respect to the advancement direction and engage slots provided below the sliders.
In this manner, the belts or chains can perform the function of moving the grip elements, and therefore the rolls, but also the function of adjusting the transverse position, since they, as well as the pulleys around which they are wound, are capable of moving transversely with respect to the advancement direction of the grip elements.
However, this solution is not free from drawbacks. The arrangement of the above-mentioned adjustment and movement means below the sliders and therefore inside the annular path along which the grip elements work generates a structural complexity that designers have to cope with during the definition of the general layout of the machine.
Moreover, the movement means must be ensured the possibility to recover the elongation that they undergo over time, be it elastic, as in the case of belts, or due to wear, as in the case of chains.
This need increases the complexity, from a structural standpoint, of the provision of such means, since they must meet the task of movement and transverse adjustment and at the same time be capable of recovering elongations.